fix i8k inline asm to avoid miscompilation with newer gcc
This commit is contained in:
Kyle McMartin
parent
15589b25c9
commit
6b5e37dd4b
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@ -0,0 +1,84 @@
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commit 22d3243de86bc92d874abb7c5b185d5c47aba323
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Author: Jim Bos <jim876@xs4all.nl>
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Date: Mon Nov 15 21:22:37 2010 +0100
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Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again)
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The fix in commit 6b4e81db2552 ("i8k: Tell gcc that *regs gets
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clobbered") to work around the gcc miscompiling i8k.c to add "+m
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(*regs)" caused register pressure problems and a build failure.
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Changing the 'asm' statement to 'asm volatile' instead should prevent
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that and works around the gcc bug as well, so we can remove the "+m".
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[ Background on the gcc bug: a memory clobber fails to mark the function
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the asm resides in as non-pure (aka "__attribute__((const))"), so if
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the function does nothing else that triggers the non-pure logic, gcc
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will think that that function has no side effects at all. As a result,
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callers will be mis-compiled.
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Adding the "+m" made gcc see that it's not a pure function, and so
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does "asm volatile". The problem was never really the need to mark
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"*regs" as changed, since the memory clobber did that part - the
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problem was just a bug in the gcc "pure" function analysis - Linus ]
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Signed-off-by: Jim Bos <jim876@xs4all.nl>
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Acked-by: Jakub Jelinek <jakub@redhat.com>
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Cc: Andi Kleen <andi@firstfloor.org>
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Cc: Andreas Schwab <schwab@linux-m68k.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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commit 6b4e81db2552bad04100e7d5ddeed7e848f53b48
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Author: Jim Bos <jim876@xs4all.nl>
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Date: Sat Nov 13 12:13:53 2010 +0100
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i8k: Tell gcc that *regs gets clobbered
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More recent GCC caused the i8k driver to stop working, on Slackware
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compiler was upgraded from gcc-4.4.4 to gcc-4.5.1 after which it didn't
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work anymore, meaning the driver didn't load or gave total nonsensical
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output.
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As it turned out the asm(..) statement forgot to mention it modifies the
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*regs variable.
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Credits to Andi Kleen and Andreas Schwab for providing the fix.
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Signed-off-by: Jim Bos <jim876@xs4all.nl>
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Cc: Andi Kleen <andi@firstfloor.org>
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Cc: Andreas Schwab <schwab@linux-m68k.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
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index 3bc0eef..d72433f 100644
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--- a/drivers/char/i8k.c
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+++ b/drivers/char/i8k.c
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@@ -120,7 +120,7 @@ static int i8k_smm(struct smm_regs *regs)
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int eax = regs->eax;
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#if defined(CONFIG_X86_64)
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- asm("pushq %%rax\n\t"
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+ asm volatile("pushq %%rax\n\t"
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"movl 0(%%rax),%%edx\n\t"
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"pushq %%rdx\n\t"
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"movl 4(%%rax),%%ebx\n\t"
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@@ -146,7 +146,7 @@ static int i8k_smm(struct smm_regs *regs)
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: "a"(regs)
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: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
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#else
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- asm("pushl %%eax\n\t"
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+ asm volatile("pushl %%eax\n\t"
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"movl 0(%%eax),%%edx\n\t"
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"push %%edx\n\t"
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"movl 4(%%eax),%%ebx\n\t"
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@@ -167,7 +167,8 @@ static int i8k_smm(struct smm_regs *regs)
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"movl %%edx,0(%%eax)\n\t"
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"lahf\n\t"
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"shrl $8,%%eax\n\t"
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- "andl $1,%%eax\n":"=a"(rc)
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+ "andl $1,%%eax\n"
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+ :"=a"(rc)
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: "a"(regs)
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: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
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#endif
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@ -728,6 +728,8 @@ Patch12305: xhci_hcd-suspend-resume.patch
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Patch12307: tty-restore-tty_ldisc_wait_idle.patch
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Patch12308: fix-i8k-inline-asm.patch
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%endif
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BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
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@ -1350,6 +1352,8 @@ ApplyPatch xhci_hcd-suspend-resume.patch
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ApplyPatch tty-restore-tty_ldisc_wait_idle.patch
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ApplyPatch fix-i8k-inline-asm.patch
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# END OF PATCH APPLICATIONS
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%endif
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@ -1963,6 +1967,10 @@ fi
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# || ||
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%changelog
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* Tue Nov 23 2010 Kyle McMartin <kyle@redhat.com>
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- fix-i8k-inline-asm.patch: backport gcc miscompilation fix from git
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[22d3243d, 6b4e81db] (rhbz#647677)
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* Mon Nov 22 2010 Kyle McMartin <kyle@redhat.com>
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- Add a debugging patch to help track down which tty is being
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poked by plymouth.
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